In the prior art, the typical passive infrared (IR) fuze design, for use on a guided missile against airborne targets, has two detection beams separated by some rather large angle, with one of these beams directed into the forward hemisphere ahead of the warhead expansion volume. The time relationships between signals in the two beams is processed to determine whether or not a detonation signal should be delivered to the warhead. This type of passive IR fuzing is susceptible to countermeasures in the form of "towed decoys" or properly deployed pyrotechnic flares.